1. Field of the Invention
The present invention relates to a laser diode module which is suitably used in the field of optical communications and optically couples a laser diode to an optical fiber.
2. Description of the Related Art
A laser diode module (hereinafter called xe2x80x9cLD modulexe2x80x9d) in which a laser diode (hereinafter abbreviated as xe2x80x9cLDxe2x80x9d) and an optical fiber are optically coupled to each other in a manner of condensing a laser beam from the LD on an inlet end face of the optical fiber through a lens. The optical fiber delivers the received laser beam from an outlet end face thereof. At the time of manufacturing an LD module, alignment including optical axis alignment and focus point adjustment among the LD, the lens and the optical fiber is carried out with a precision of 1 xcexcm or less in order to acquire the desired optical output. The alignment is executed while monitoring the optical output of the LD module. That is, to acquire the maximum amount of light from the outlet end face of the optical fiber, the inlet end face of the optical fiber is positioned at the focal point of the lens where the laser beam is condensed. The aim of such alignment is to minimize the adverse influence of a variation in the working precision of the constituting members with respect to the performance of the LD module.
When the support members that support the constituting elements of the LD module, such as the LD, the lens and the optical fiber, are heated due to the heat generation of the LD itself or a rise in the environmental temperature of the LD module, those support members thermally expand, deviating the relative positions of the LD, the lens and the optical fiber that have been aligned in the order of microns. The deviation in the relative positions lowers the optical coupling efficiency between the LD and the optical fiber (hereinafter simply called xe2x80x9coptical coupling efficiencyxe2x80x9d) and results in reduction of the optical output of the LD module. Specifically, the temperature of the support members comes in a range of 60xc2x0 C. to 90xc2x0 C., for example, the optical output of the LD module declines prominently. The reduction in the optical output of the LD module may disable optical communications using the LD module.
To cope with the problem, a typical LD module is equipped with a temperature control device, such as a Peltier device. The temperature control device discharges the thermal energy originated from the heat generation of the LD or a rise in environmental temperature out of the LD module.
However, the LD module equipped with a temperature control device has following shortcomings. First, because of the large size, this type of LD module cannot be housed in a package for a communication transceiver which demands miniaturization. Further, the LD module needs a power source for driving the temperature control device or the Peltier device and an external control circuit for controlling the operation of the Peltier device. The power source and external control circuit result in an increase in the cost of the LD module.
Moreover, when the performance of the temperature control device is insufficient, the temperature of the LD module, i.e., the temperature of the support members inevitably rises.
Accordingly, it is an object of the present invention to provide an LD module which suppresses a reduction in optical output originated from the heat generation of an LD or a rise in ambient temperature and whose cost reduction and miniaturization can be achieved.
A laser diode module according to the present invention comprises a laser diode having an end face from which a laser beam is emitted; a lens which has an input-side principal plane and an output-side principal plane, and condenses the laser beam from the laser diode at a focal point thereof; an optical fiber having an end face for receiving the laser beam condensed by the lens and delivering the received laser beam as an output of said module; and support means for supporting the laser diode, the lens and the optical fiber and securing an inlet distance between the end face of the laser diode and the input-side principal plane of the lens and an outlet distance between the output-side principal plane of the lens and the end face of the optical fiber. The support means positions the end face of the optical fiber at a deviation position apart from the focal point of the lens by an allowable distance with respect to the output of said module when a temperature of the laser diode module is room temperature and moves the end face of the optical fiber at a close position relatively closer to the focal point than the deviation position when the temperature of the laser diode module rises from the room temperature.